The present invention relates generally to a system for enhancing plant growth under field conditions. Although the teachings of this invention may be used to increase the rate of plant growth in a wide number of applications, the invention is particularly well suited for use in reforestation of land.
It is well known that plants utilize carbon dioxide in the surrounding atmosphere as a source of carbon from which the complex organic molecules making up the plant are formed. Plants absorb the carbon dioxide through stomates in their leaves and release free oxygen after the photosynthesis process breaks the carbon dioxide into its component elements.
It has long been known that the growth rate of plants generally bears a proportional relationship to the concentration of carbon dioxide in the ambient atmosphere--a low carbon dioxide concentration tends to stunt the growth of the plant while an enhanced carbon dioxide concentration can significantly increase the rate at which the plants grow. Under normal atmospheric conditions, air generally comprises about 78% nitrogen, about 21% oxygen and only about 0.03% carbon dioxide, with the balance being made up of a number of trace gases. By significantly increasing this minimal carbon dioxide concentration adjacent the vegetation, one would expect to see a correspondingly significant increase in the vegetation's rate of development.
This relationship between carbon dioxide concentration and the growth rate of plants has been exploited for quite some time in greenhouse environments. For examples of greenhouse systems which utilize enhanced carbon dioxide concentration, see, e.g., U.S. Pat. Nos. 3,999,329 (Brais), 4,028,847 (Davis, et al), and 4,073,089 (Maginnes, et al). Although this technique seems to work quite well in an enclosed environment, such as that presented by a greenhouse, utility of this technique of growing plants under field conditions is severely limited.
When growing plants out-of-doors, it has heretofore been very impractical to supply gaseous carbon dioxide over large areas. When gaseous carbon dioxide is supplied under field conditions, the carbon dioxide becomes diluted by the ambient atmosphere and blown away by the wind. Some inventors have attempted to circumvent these difficulties by dissolving high concentrations of carbon dioxide in aqueous solution and spraying this solution directly on the plants. (See, e.g., U.S. Pat. No. 4,689,067, issued to Kuckens, et al.) As the water evaporates or is absorbed by the plants, gaseous carbon dioxide is liberated very near the stomates. By releasing the carbon dioxide in such close proximity to the stomates, the dilutive effects of the atmosphere and the tendency of wind to carry off the carbon dioxide are minimized. For an example of such a method see U.S. Pat. No. 4,689,067 (Kuckens et al)
As plants absorb carbon dioxide from the ambient air, the supply of carbon dioxide in that air is obviously diminished. Under many field conditions, such as those most commonly encountered in fields of commercially-grown agricultural products, there is sufficient circulation of air adjacent the plants to ensure a relatively constant supply of carbon dioxide to the entire leaf system of the plant. In certain circumstances, however, there is insufficient circulation of air across the plants.
Limited air circulation is most often encountered in situations where the plants grow closely to one another and tend to form a "closed canopy" of interlocking branches or limbs that tend to inhibit the passage of air therethrough. When this occurs, the leaves on a plant which are positioned generally above the "canopy" are exposed to the ambient air and receive a continually replenished supply of carbon dioxide. However, leaves which are located below the canopy must scavenge carbon dioxide from the air underneath the canopy. Since the canopy itself tends to limit recirculation of the air supply, the level of carbon dioxide beneath the canopy is reduced quite rapidly. Under many circumstances, such as those encountered in many forests, this tends to choke off the lower leaves and their associated branches, which effectively precludes any contribution to the growth of the plant as a whole from these lower leaves.
Although it would be possible to spray plants which grow into a closed canopy with an aqueous carbon dioxide solution, as suggested by the prior art, this would not be practical for many applications. This approach would be particularly inappropriate for plants such as trees wherein the cost of continuously spraying the entire plant with the solution could greatly outweigh the increased yield.